I am facing the same issue with access to Google Drive links only that the links are internal to the company. The documents are still accessible from directly from Google Drive but trying to access them from Asana pops up the “Error Forbidden” message.
@Eduardo-Mussali@Codrut - do either of you have admin rights in your Asana instance (or the ear of someone who does)? Perhaps you could try re-authenticating the app. You can also create a support ticket with Asana by following these steps.